The present invention relates to a control system of an automatic transmission having a torque converter for a motor vehicle driven by an alcohol engine using a mixed fuel of alcohol and gasoline (flexible fuel vehicle), and more particularly to the control system for controlling a lockup system of the torque converter in dependency on concentration of the alcohol in the fuel.
In the alcohol engine which is controlled in maximum efficiency, the calorific value of the alcohol is slightly larger than that of the gasoline in a theoretical air fuel ratio and the flaming speed of the alcohol is higher than the flaming speed of the gasoline. Consequently, as the concentration of the alcohol in the fuel increases, the ignition timing of the engine approaches a top dead center so that thermal efficiency is increased, thereby increasing engine power.
However, since engine performance changes in accordance with change of the alcohol concentration, a driver feels uncomfortable when the alcohol concentration changes.
Fuel consumption of the alcohol engine is larger than that of the gasoline engine.